Postage meters are mass produced devices for printing a defined unit value for governmental or private carrier delivery of parcels and envelopes. The term postage meter also includes other like devices which provide unit value printing such as tax stamp meters. Postage meters include internal accounting devices which account for postage value representation which is stored within the meter. The accounting device accounts for both the recharging of the meter with additional postage value and the printing of postage by the meter printing mechanism. No external independent accounting system is available for accounting for the postage printed by the meter. Accordingly, postage meters must possess a high reliability to avoid the loss of user or governmental funds stored within the meter and dispensed by printing postage.
Electronic postage meters have been developed and are disclosed, for example, in U.S. Pat. No. 3,978,457 for MICROCOMPUTERIZED ELECTRONIC POSTAGE METER SYSTEM; in U.S. Pat. No. 4,301,507 for ELECTRONIC POSTAGE METER HAVING PLURAL COMPUTING SYSTEMS; and, in U.S. Pat. No. 4,484,307, for ELECTRONIC POSTAGE METER HAVING IMPROVED SECURITY AND FAULT TOLERANCE FEATURES. Such meters have electronic accounting circuits which include electronic non-volatile memory capability for storing postage accounting information. The accounting circuits and associated postage printing mechanism are physically sealed within a tamper resistant enclosure. The non-volatile memories are provided for storing critical postage accounting information when external operating power is not applied to the meter.
Various types of accounting information may be stored in the meter non-volatile memory. This information includes, for example, the total amount of postage remaining in the meter for subsequent printing (descending register) and the total amount of postage printed by the meter (ascending register). Other types of accounting or operating data may also be stored. For example, service information in the form of error codes denoting various types of malfunctions or abnormal conditions encountered during operation of the meter may be stored in non-volatile memories. This facilitates the evaluation of the operating experience of each meter to assist in its repair, should that be necessary, and to accumulate data helpful in the design of electronic postage meters.
Non-volatile memories as well as the other electronic accounting circuitry within electronic postage meters are susceptible to disturbances which can either destroy information or cause erroneous information to be generated. The electronic circuits are susceptible to electromagnetic radiation and electrical transients which can interfere with the proper operation of the meter and accurate storage of information. These types of effects can result in a loss of funds to the users and, accordingly, it has been recognized that various types of protection must be provided to avoid such undesirable results as the data cannot be reconstructed in most instances from other externally available records.
Electronic postage meters of the type that write to nonvolatile memories only during power down sequence such as disclosed in above identified U.S. Pat. No. 4,301,507, operates satisfactorily for their intended purposes. However, if a difficulty occurs during the several millisecond when external power is removed and the capacitance within the system provides the power to write, critical accounting information may be lost. This information may not be able to be reconstructed because it is not stored in other nonvolatile memories.
Systems have also been developed, such as disclosed in U.S. Pat. No. 4,484,307 for ELECTRONIC POSTAGE METER HAVING IMPROVED SECURITY AND FAULT TOLERANCE FEATURES, and published European Patent Application, Publication No. 0 085 385 for MICROPROCESSOR SYSTEMS FOR ELECTRONIC POSTAGE METERS which have memories wherein data is written into nonvolatile memories during each operation of the meter. Other electronic postage meter systems, such as disclosed in U.S. patent application of Wallace Kirschner, Easwaran C. N. Nambudiri and Douglas H. Patterson, Ser. No. 643,219, filed Aug. 22, 1984, for NONVOLATILE MEMORY SYSTEM WITH REAL TIME AND POWER DOWN DATA STORAGE CAPABILITY FOR AN ELECTRONIC POSTAGE METER, where dual nonvolatile memories are employed, one wherein data is written during each operation of the meter and another wherein data is written only during a power down sequence.